U.S. patent application number 14/052228 was filed with the patent office on 2014-04-17 for multi-ion sensor.
This patent application is currently assigned to HORIBA, Ltd.. The applicant listed for this patent is HORIBA, Ltd.. Invention is credited to Yasukazu IWAMOTO, Hiromi OHKAWA.
Application Number | 20140105788 14/052228 |
Document ID | / |
Family ID | 49303840 |
Filed Date | 2014-04-17 |
United States Patent
Application |
20140105788 |
Kind Code |
A1 |
IWAMOTO; Yasukazu ; et
al. |
April 17, 2014 |
MULTI-ION SENSOR
Abstract
In order to provide a planar type multi-ion sensor which is
easily thinned and has high measurement accuracy, a multi-ion
sensor 1 adapted to measure a concentration ratio of sodium ions to
potassium ions in a sample solution, includes: a sodium ion
electrode 41 selectively reacting to the sodium ions; a potassium
ion electrode 42 selectively reacting to the potassium ions; and a
common electrode 28 in contrast with the sodium ion electrode 41
and the potassium ion electrode 42, wherein the sodium ion
electrode 41, potassium ion electrode 42 and common electrode 28
are provided on the same support body, the common electrode 28 does
not include internal solution, and the concentration ratio of the
sodium ions to the potassium ions is measured based on a variable A
that is obtained by the following Equation (1), Fig . 7 A = E Na Q
.times. .alpha. Na - E K Q .times. .alpha. K ( 1 ) ##EQU00001##
Inventors: |
IWAMOTO; Yasukazu;
(Kyoto-shi, JP) ; OHKAWA; Hiromi; (Kyoto-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HORIBA, Ltd. |
Kyoto-shi |
|
JP |
|
|
Assignee: |
HORIBA, Ltd.
Kyoto-shi
JP
|
Family ID: |
49303840 |
Appl. No.: |
14/052228 |
Filed: |
October 11, 2013 |
Current U.S.
Class: |
422/82.02 |
Current CPC
Class: |
G01N 27/4035 20130101;
G01N 33/492 20130101; G01N 27/27 20130101; G01N 27/333 20130101;
G01N 27/307 20130101; G01N 27/3272 20130101 |
Class at
Publication: |
422/82.02 |
International
Class: |
G01N 31/00 20060101
G01N031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 11, 2012 |
JP |
2012-226286 |
Claims
1. A multi-ion sensor adapted to measure a concentration ratio of
sodium ions to potassium ions in a sample solution, comprising: a
sodium ion electrode selectively reacting to the sodium ions; a
potassium ion electrode selectively reacting to the potassium ions;
and a common electrode in contrast with the sodium ion electrode
and the potassium ion electrode, wherein the sodium ion electrode,
potassium ion electrode and common electrode are provided on the
same support body, the common electrode does not include internal
solution, and the multi-ion sensor is configured so as to measure
the concentration ratio of the sodium ions to the potassium ions
based on a variable A that is obtained by the following Equation
(1), A = E Na Q .times. .alpha. Na - E K Q .times. .alpha. K ( 1 )
##EQU00013## in Equation (1), E.sub.Na represents a potential of
the sodium ion electrode, E.sub.K represents a potential of the
potassium ion electrode, Q represents a Nernst coefficient,
.alpha..sub.Na represents a sensitivity coefficient of the sodium
ion electrode, and .alpha..sub.K represents a sensitivity
coefficient of the potassium ion electrode.
2. The multi-ion sensor according to claim 1, wherein the
sensitivity coefficients .alpha..sub.Na and .alpha..sub.K are
1.
3. The multi-ion sensor according to claim 1, wherein the
sensitivity coefficients .alpha..sub.Na and .alpha..sub.K are
coefficients determined by calibration.
4. The multi-ion sensor according to claim 1, wherein an Ag/AgCl
electrode is used as the common electrode, the sensitivity
coefficients .alpha..sub.Na and .alpha..sub.K are 1, and the
multi-ion sensor is configured so as to measure the concentration
of the sodium ions by the following Equation (2) and measure the
concentration of the potassium ions by the following Equation (3),
C Na = 10 ^ ( ( E Na - E C l ) 2 .times. F 2.303 RT + log C 0 Na )
( 2 ) C K = C o K 10 ^ ( A ) .times. C 0 Na .times. C Na ( 3 )
##EQU00014## in Equations (2) and (3), A is a value obtained by
Equation (1), E.sub.Cl represents a potential of the common
electrode, C.sub.Na represents the concentration of the sodium
ions, C.sub.K represents the concentration of the potassium ions,
C.sub.0Na represents the concentration of the sodium ions subjected
to zero calibration, C.sub.0K represents the concentration of the
potassium ions subjected to zero calibration, F represents a
Faraday constant, R represents a gas constant, and T represents a
temperature.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present invention claims priority under 35 U.S.C.
.sctn.119 to Japanese Application No. 2012-226286 filed Oct. 11,
2012, the entire content of which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates to a multi-ion sensor for
measuring a concentration ratio between sodium ions and potassium
ions.
BACKGROUND ART
[0003] In a human body, intracellular and extracellular osmotic
pressures are kept constant and an action of kidney is properly
maintained by an ion balance between sodium and potassium. However,
in our eating habits of frequently using processed foods today,
there is a tendency of an intake amount of sodium being large and
an intake amount of potassium being reduced. Therefore, it is
effective for management of a health condition to measure a ratio
of Na/K.
[0004] A multi-ion sensor capable measuring concentrations of
sodium ions and potassium ions in such as beverage is known as
shown in, for example, Patent Literature 1. However, in the
multi-ion sensor described in Patent Literature 1, after a
concentration of sodium ions and a concentration of potassium ions
are separately measured, a concentration ratio of sodium ions to
potassium ions is obtained based on these measurement values.
[0005] In this multi-ion sensor configured to obtain a
concentration ratio of sodium ions to potassium ions based on these
measurement values after a concentration of sodium ions and a
concentration of potassium ions are separately measured, it is
necessary to present a constant reference potential to each of a
sodium ion electrode and potassium ion electrode. Therefore,
internal solution is required for a reference electrode. Therefore,
it has been conventionally difficult to reduce a thickness of a
multi-ion sensor integrally provided with a reference electrode to
be thinner.
CITATION LIST
Patent Literature
[0006] Patent Literature 1: JPA-Sho-63-181749
SUMMARY OF INVENTION
Technical Problem
[0007] Therefore, the present invention has been made intending to
provide a planar type multi-ion sensor that is easily thinned and
has high measurement accuracy.
Solution to Problem
[0008] That is, a multi-ion sensor according to the present
invention is adapted to measure a concentration ratio of sodium
ions to potassium ions in a sample solution, and this multi-ion
sensor includes: a sodium ion electrode selectively reacting to the
sodium ions; a potassium ion electrode selectively reacting to the
potassium ions; and a common electrode in contrast with the sodium
ion electrode and the potassium ion electrode, wherein the sodium
ion electrode, potassium ion electrode and common electrode are
provided on the same support body, the common electrode does not
include internal solution, and the multi-ion sensor is configured
so as to measure the concentration ratio of the sodium ions to the
potassium ions based on a variable A that is obtained by the
following Equation (1).
A = E Na Q .times. .alpha. Na - E K Q .times. .alpha. K ( 1 )
##EQU00002##
[0009] In Equation (1), E.sub.Na represents a potential of the
sodium ion electrode, E.sub.K represents a potential of the
potassium ion electrode, Q represents a Nernst coefficient,
.alpha..sub.Na represents a sensitivity coefficient of the sodium
ion electrode, and .alpha..sub.K represents a sensitivity
coefficient of the potassium ion electrode.
[0010] In the case where Equation (1) is represented while
including a potential E.sub.com of the common electrode, it is
represented as the following Equation (1)'. However, since the
potential of the common electrode is canceled, even if the
potential of the common electrode is varied, it does not affect the
measurement result of the concentration ratio between the sodium
ions and the potassium ions.
A = ( E Na Q .times. .alpha. Na - E com ) - ( E K Q .times. .alpha.
K - E com ) ( 1 ' ) ##EQU00003##
[0011] Therefore, according to the present invention, since the
measurement result of the concentration ratio between the sodium
ions and the potassium ions is not affected even if the potential
of the common electrode is varied, the potential of the common
electrode under measurement may be varied but not be constant.
Thus, the internal solution for the common electrode is unnecessary
and therefore the sensor can be easily thinned.
[0012] Further, since the concentration ratio between the sodium
ions and the potassium ions is measured based on the potential
difference between the sodium ions and the potassium ions using
respective sensitivity coefficients of the sodium ion electrode and
the potassium ion electrode, even though these sensitivity
coefficients are varied, the concentration ratio between the sodium
ions and the potassium ions can be accurately measured.
[0013] The sensitivity coefficients .alpha..sub.Na and
.alpha..sub.K may be 1 or may be determined by calibration. In the
case where the sensitivity coefficients .alpha..sub.Na and
.alpha..sub.K are 1, "Q.times..alpha..sub.Na," and
"Q.times..alpha..sub.K" become Nernst coefficient Q represented by
the following equation, and this becomes a theoretical slope which
is 59.16 mV at a temperature of 25.degree. C.
Q = 2.303 RT F ##EQU00004##
[0014] Meanwhile, in the case where the sensitivity coefficients
.alpha..sub.Na and .alpha..sub.K are determined by calibration,
"Q.times..alpha..sub.Na" and Q.times..alpha..sub.K" become
practical slopes to be described later.
[0015] In addition, when a solution such as a drink containing
sodium chloride is measured using Ag/AgCl containing chloride ions
as the common electrode, it can be assumed in some cases that a
chloride ion concentration is equal to a sodium ion concentration
in quantity. In this case, the reference potential E.sub.0 can be
obtained by reducing the potential difference between the potential
E.sub.Cl of the common electrode and the potential E.sub.Na of the
sodium ion electrode to be half.
E 0 = E Na - E C l 2 ##EQU00005##
[0016] Therefore, the concentration of sodium ions can be obtained
from Equation (2) using this reference potential.
C Na = 10 ^ ( ( E Na - E C l ) 2 .times. F 2.303 RT + log C 0 Na )
( 2 ) ##EQU00006##
[0017] The concentration of the potassium ions can be obtained from
Equation (3) using the concentration of the sodium ions obtained
from Equation (2) and the concentration ratio between the sodium
ions and the potassium ions measured based on the variable A
obtained by Equation (1).
C K = C oK 10 ^ ( A ) .times. C 0 Na .times. C Na ( 3 )
##EQU00007##
[0018] In Equations (2) and (3), A represents a value obtained by
Equation (1), E.sub.Cl represents a potential of the common
electrode, C.sub.Na represents the concentration of the sodium
ions, C.sub.K represents the concentration of the potassium ions,
C.sub.0Na represents the concentration of the sodium ions subjected
to zero calibration, C.sub.0K represents the concentration of the
potassium ions subjected to zero calibration, F represents a
Faraday constant, R represents a gas constant, and T represents a
temperature.
[0019] Therefore, in the multi-ion sensor according to the present
invention, assuming that the sensitivity coefficients
.alpha..sub.Na and .alpha..sub.K are 1 while using Ag/AgCl as the
common electrode, the concentrations of the sodium ions and
potassium ions can be calculated.
Advantageous Effects of Invention
[0020] Thus, according to the present invention, there can be
obtained a planar type multi-ion sensor which can be easily thinned
and has high measurement accuracy.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is an overall schematic view of a multi-ion sensor
according to a first embodiment of the present invention;
[0022] FIG. 2 is an overall schematic view of the multi-ion sensor
according to the same embodiment;
[0023] FIG. 3 is an exploded perspective view showing a planar
sensor in the same embodiment;
[0024] FIG. 4 is a cross sectional view taken along a line A-A' in
FIG. 2;
[0025] FIG. 5 is a schematic view showing a manufacturing process
of a multi-ion sensor according to the same embodiment;
[0026] FIG. 6 is an exploded perspective view showing a planar
sensor in another embodiment; and
[0027] FIG. 7 is an exploded perspective view showing a planar
sensor according to a second embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0028] The following describes a first embodiment of the present
invention referring to the accompanying drawings.
[0029] A multi-ion sensor 1 according to the first embodiment is
composite typed one including liquid membrane type ion-selective
electrodes for measuring a concentration ratio of sodium ions to
potassium ions in a sample solution and a common electrode
integrated therewith. As shown in FIGS. 1 and 2, the multi-ion
sensor 1 is comprised of a main body 2 made of synthetic resin, a
display/operation part 3 formed on an upper surface of the main
body 2 and a planar sensor 4 provided on a distal end side of the
main body 2.
[0030] An arithmetic processing unit such as a microcomputer and a
power supply part (either not shown) are incorporated in the main
body 2. An insertion opening 2B is formed in a distal end surface
of the main body 2 in order for inserting lead portions 21A, 22A
and 25A of the planar sensor 4, and by inserting the lead portions
21A, 22A and 25A of the planar sensor 4 into the insertion opening
2B, the lead portions 21A, 22A and 25A are connected to a circuit
board constituting the arithmetic processing unit incorporated in
the main body 2.
[0031] The display/operation part 3 is comprised of a display unit
31 and an operation part 32 including various kinds of operation
buttons such as a power button 32a, a calibration button 32b and a
hold button 32c.
[0032] The planar sensor 4 is configured so as to be integrally
connected with the main body 2 by inserting the lead portions 21A,
22A and 25A into the insertion opening 2B or to be detachable from
the main body 2. As shown in FIG. 3, the planar sensor 4 is made of
a material having electrically insulating properties such as, for
example, polyethylene terephthalate (referred to as "PET"
hereinafter) and includes first to third substrates 11, 12 and 13
which are mutually laminated. Each of the substrates 11, 12 and 13
has a thickness in a degree of 300 .mu.m and each distal end
portion thereof is formed to be arcuate. Further, a test solution
holder 74 is formed at a distal end of the third substrate 13 so as
to surround a periphery of the second substrate 12.
[0033] On the first substrate 11, conductive parts 21, 22 and 25
are formed by performing, for example, a silk-screen printing of an
Ag paste and the like after performing a predetermined pretreatment
on the upper surface thereof. Resist processing of the conductive
parts 21, 22 and 25 is performed except for the distal end portions
thereof, and the distal end portions thereof are processed as
follows. That is, the distal end portion of one outer side
conductive part 21 is coated with AgCl to thereby form an internal
electrode 26 of a Na.sup.+ electrode 41 and the distal end portion
of the other outer side conductive part 22 is also coated with AgCl
to thereby form an internal electrode 27 of a K.sup.+ electrode 42.
Also, the distal end portion of the inner side conductive part 25
is coated with AgCl to thereby form a common electrode 28. Then,
the rear end portions of the conductive parts 21, 22 and 25
respectively constitutes the lead portions 21A, 22A and 25A as they
are.
[0034] Further, as shown in FIG. 6, there may be provided a
temperature compensation element 29 such as a thermistor on the
first substrate 11. In FIG. 6, reference numerals 23 and 24 denote
conductive parts which are connected to the temperature
compensation element 29, reference numerals 23A and 24A denote lead
portions configured of the rear end portions of the conductive
parts 23 and 24, and reference numeral 85 denotes a rectangular
through hole formed at a position in the second substrate 12
corresponding to the temperature compensation element 29, wherein
the through hole 85 has a size substantially the same as the
temperature compensation element 29. As shown in FIG. 3, in the
case where there is not provided a temperature compensation element
such as a thermistor, a constant (for example, 25.degree. C.
(=298.15K)) is used as T for calculating the Nernst coefficient
Q.
[0035] In the second substrate 12, there are provided through holes
83 and 84 formed at positions corresponding to the internal
electrodes 26 and 27, respectively, so as to have substantially the
same shapes as those of the internal electrodes 26 and 27, and
further there is provided a through hole 82 formed at a position
corresponding to the common electrode 28 so as to have
substantially the same shape as that of the common electrode
28.
[0036] Gel internal solutions 14a and 14b are respectively filled
in the through holes 83 and 84 formed in the second substrate 12.
The gel internal solution 14a is obtained in a process of, firstly
making an internal solution added with NaCl, subsequently further
adding agar as a gelling agent and glycerin as a gel evaporation
inhibitor to the internal solution, and then curing the resultant
internal solution. Similarly, the gel internal solution 14b is
obtained in a process of, firstly making an internal solution added
with KCl, subsequently further adding agar as a gelling agent and
glycerin as a gel evaporation inhibitor to the internal solution,
and then curing the resultant internal solution. Moreover, in order
to adjust chloride ion concentrations of the gel internal solutions
14a and 14b, CaCl.sub.2 may be further added. In addition, the
chloride ion concentration of the internal solution may be adjusted
to be in a degree of 0.05 to 1 M and may be combined with a
chloride ion concentration of a sample and also may be combined
with a chloride ion concentration of a calibration solution.
However, in the case where CaCl.sub.2 is not added, the chloride
ion concentration of the internal solution is adjusted to be in a
degree of 0.1 M. In particular, in the case where the chloride ion
concentration of the internal solution is combined with a chloride
ion concentration of a calibration solution, since the calibration
solution may be used as a preservative solution, the chloride ion
concentration of the internal solution may be stabilized for a long
term and it is also possible to immediately perform a calibration.
Meanwhile, as shown in FIG. 4, gel internal solution is not filled
in the through hole 82 formed in the second substrate 12.
[0037] A sodium ion sensitive membrane 15 and potassium ion
sensitive membrane 16 are further mounted on the gel internal
solutions 14a and 14b in the through holes 83 and 84, respectively,
formed in the second substrate 12 so as to be in contact with the
gel internal solutions 14a and 14b and fixed to be substantially
coplanar with the upper surface of the second substrate 12.
[0038] The sodium ion sensitive membrane 15 is obtained in a
process of: adding a plasticizer and sodium ionophore to polyvinyl
chloride (PVC) and then dissolving the same with an organic solvent
such as tetrahydrofuran (referred to as "THF" hereinafter), then
filling the resultant solution into the through hole 83 by such as
a potting or inkjet printing method, and thereafter evaporating the
organic solvent by heating to thereby form a solid state sodium ion
sensitive membrane 15.
[0039] The potassium ion sensitive membrane 16 is formed in the
same manner as the sodium ion sensitive membrane 15, except for
using potassium ionophore.
[0040] FIG. 5 shows a manufacturing procedure of the planar sensor
4 having such a configuration. First, the first substrate 11 having
the conductive parts 21, 22 and 25 formed thereon, second
substrates 12 and third substrate 13 are laminated via an adhesive
(see FIG. 5(a)) to obtain a laminated body. The obtained laminated
body is subjected to such as a roller and firmly bonded (see FIG.
5(b)). Next, AgCl is formed at a distal end portion of each of the
conductive parts 21, 22 and 25 by such as a dipping method through
the through holes 82, 83 and 84 provided in the second substrate
12, thereby forming the common electrode 28, internal electrode 26
of the Na.sup.+ electrode 41 and internal electrode 27 of the
K.sup.+ electrode 42 (see FIG. 5(c)). Further, the gel internal
solutions 14a and 14b are filled in the through holes 83 and 84
(see FIG. 5(d)), and then the sodium ion sensitive membrane 15 and
potassium ion sensitive membrane 16 are mounted on the gel internal
solutions 14a and 14b in the through holes 83 and 84, respectively
(see FIG. 5(e)). At this time, THF is contained in the composition
for the sodium ion sensitive membrane 15 and potassium ion
sensitive membrane 16 and this THF dissolves the PET and the like
composing the second substrate 12, whereby the sodium ion sensitive
membrane 15 and potassium ion sensitive membrane 16 and the second
substrate 12 are firmly fixed.
[0041] In order to measure a concentration ratio of sodium ions to
potassium ions in a sample solution using the multi-ion sensor 1,
first, drops of an appropriate amount of the sample solution is
applied onto the common electrode 28, sodium ion sensitive membrane
15 and potassium ion sensitive membrane 16. Then, in the sodium ion
sensitive membrane 15 and potassium ion sensitive membrane 16,
there are generated electromotive forces corresponding to
differences of the ion concentrations between the gel internal
solutions 14a, 14b and the sample solution, respectively. These
electromotive forces are detected as potential differences
(voltages) of the internal electrode 26 of the Na.sup.+ electrode
41, internal electrode 27 of the K.sup.+ electrode 42 and the
common electrode 28 to thereby calculate ratios between these
potential differences and respective practical slopes (potential
differences/concentrations). The practical slope is obtained by
independently calibrating the Na.sup.+ electrode 41 and K.sup.+
electrode 42, respectively, using the same calibration solution for
zero calibration as well as span calibration of a chloride ion
concentration containing sodium ions, potassium ions, calcium
chloride as an ionic strength adjustor, and the like. Internal
solution is usually needed also for the common electrode in order
to obtain a reference potential. However, in the present
embodiment, by making activities of chloride ions of the
calibration solutions for the zero calibration and span calibration
to be equal, it is allowed to obtain the practical slope even
without the internal solution. Moreover, in the case of using such
as a platinum electrode or carbon electrode, since these electrodes
respond to also redox substance such as dissolved oxygen, the
calibration using a standard solution takes too much time until the
potential is stabilized and it is not practical. However, in the
present embodiment, by using a silver halide electrode such as an
Ag/AgCl electrode having good compatibility with such as drinks
containing sodium and potassium like sports drinks as the common
electrode, it is made possible to perform a calibration also using
a standard solution. One example of the calibration solution for
the zero calibration and span calibration is shown in Table 1 as
following.
TABLE-US-00001 TABLE 1 Concentration (M) Zero Calibration Solution
C.sub.ONa 0.1 C.sub.OK 0.02 Span Calibration Soluiton C.sub.spanNa
0.03 C.sub.spanK 0.01
[0042] Then, according to in the following Equation (4), the
concentration ratio of sodium ions to potassium ions
(C.sub.Na/C.sub.K) is calculated in the arithmetic processing unit
to be displayed in the display unit 31.
C Na / C K = ( 10 ^ ( ( E Na / SlopeNa + ) - ( E K / Slope K + ) )
) .times. ( C 0 Na / C 0 K ) = ( 10 ^ ( A ) ) .times. ( C 0 Na / C
0 K ) ( 4 ) ##EQU00008##
[0043] Each parameter in Equation (4) is as follows.
[0044] E.sub.Na: Potential of Na.sup.+ electrode 41
[0045] SlopeNa.sup.+: Practical slope of Na.sup.+ electrode 41
[0046] E.sub.K: Potential of K.sup.+ electrode 42
[0047] SlopeK.sup.+: Practical slope of K.sup.+ electrode 42
[0048] In addition, the practical slopes "SlopeNa.sup.+
(=Q.times..alpha..sub.Na)" and "SlopeK.sup.+
(=Q.times..alpha..sub.K)" are derived from in the following
Equations (5) and (6).
E span Na - E com = Q .times. .alpha. Na .times. log ( C spanNa C 0
Na ) ( 5 ) E span K - E com = Q .times. .alpha. K .times. log ( C
spanK C 0 K ) ( 6 ) ##EQU00009##
[0049] Each parameter in Equations (5) and (6) is as follows.
[0050] E.sub.spanNa: Potential of Na.sup.+ electrode 41 at a time
of span calibration
[0051] E.sub.spanK: Potential of K.sup.+ electrode 42 at a time of
span calibration
[0052] E.sub.com: Potential of common electrode 28
[0053] In the multi-ion sensor 1 according to the present
embodiment, in order to obtain the practical slope, the chloride
ion concentrations of the calibration solutions for the zero
calibration and span calibration are made constant. Thus, the
sensitivity of each of the sensors of the Na.sup.+ electrode 41 and
K.sup.+ electrode 42 can be obtained based on the potential
difference between each of the Na.sup.+ electrode 41 and K.sup.+
electrode 42 and the common electrode 28 composed of an Ag/AgCl
electrode.
[0054] Here, in the case of measuring a solution containing sodium
chloride as a measurement sample while using the Ag/AgCl electrode
as the common electrode 28, in the case where the sodium ion
concentration is substantially equal to the sodium ion
concentration in amount, the reference potential can be obtained by
rendering the potential difference between the common electrode 28
and the sodium ion electrode 41 to be half.
E 0 = E Na - E C l 2 ##EQU00010##
[0055] Each parameter in the above Equation is as follows.
[0056] E.sub.o: Reference potential
[0057] E.sub.Na: Potential of Na.sup.+ electrode 41
[0058] E.sub.Cl: Potential of common electrode 28
[0059] If the reference potential is obtained, the sodium ion
concentration can be obtained from Equation (2) as follows.
C Na = 10 ^ ( ( E Na - E C l ) 2 .times. F 2.303 RT + log C 0 Na )
( 2 ) ##EQU00011##
[0060] Thus, if the sodium ion concentration is obtained, the
potassium ion concentration can be measured by in the following
Equation (3) which is obtained by modifying Equation (4) mentioned
above for calculating a concentration ratio between the sodium ion
concentration and the potassium ion concentration. Note that, in
the following Equation (3), it is assumed that sensitivity
coefficients .alpha..sub.Na and .alpha..sub.K in obtaining A are
1.
C K = C o K 10 ^ ( A ) .times. C 0 Na .times. C Na ( 3 )
##EQU00012##
[0061] Note that each parameter in the above Equations (2) and (3)
is as follows.
[0062] A: Variable obtained by Equation (1)
[0063] F: Faraday constant
[0064] R: Gas constant
[0065] T: Temperature
[0066] In the multi-ion sensor 1 according to the present
embodiment configured as described above, even though the potential
of the common electrode 28 is varied, the variation does not affect
the measurement result of the concentration ration between the
sodium ions and the potassium ions. Therefore, the potential of the
common electrode 28 may be varied but not be constant. Therefore,
since the internal solution is not required for the common
electrode 28, the sensor 1 can be easily reduced in thickness.
[0067] In addition, since the concentration ration between the
sodium ions and the potassium ions is measured using the respective
practical slopes of the Na.sup.+ electrode 41 and K.sup.+ electrode
42, even though these slopes are varied, the concentration ration
between the sodium ions and the potassium ions can be measured
accurately.
[0068] Furthermore, since the Ag/AgCl electrode is used as the
common electrode 28, the variation in potential is small even
without internal solution and it is possible to deal with also
sodium ions and potassium ions of having the concentrations largely
changed in the sample solution. In addition, as the common
electrode 28, an Ag/AgBr electrode or Ag/AgI electrode can be also
used other than the Ag/AgCl electrode.
[0069] In addition, in the case where the Ag/AgCl electrode is used
as the common electrode 28, the sodium ion concentration and
potassium ion concentration can be calculated.
[0070] Next, the following describes a second embodiment referring
to an accompanying drawing of FIG. 7.
[0071] In the multi-ion sensor 1 according to the second
embodiment, the configuration of the conductive part formed on the
first substrate 11 is different from that of the first embodiment.
Note that the same reference numerals are given to the same parts
as the first embodiment and the explanations thereof are omitted
here.
[0072] As shown in FIG. 7, conductive parts 121, 122 and 125 are
formed on the first substrate 11 by performing, for example, a
silk-screen printing of an Ag paste and the like so that the
conductive part 125 surrounds the conductive parts 121 and 122.
Distal end portions of the conductive parts 121 and 122 are coated
with AgCl to thereby form internal electrodes 26 and 27 of the
Na.sup.+ electrode 41 and K.sup.+ electrode 42, respectively. A
partial portion of the conductive part 125 formed so as to surround
the conductive parts 121 and 122 is coated with AgCl to form a
common electrode 28. The conductive parts 121, 122 and 125 except
for the portions where the electrodes are formed are subjected to
resist processing. Then, the rear end portions of the conductive
parts 121, 122 and 125 constitute lead portions 121A, 122A and
125A, respectively.
[0073] In the multi-ion sensor 1 according to the second embodiment
configured as described above, since the conductive part 125 acts
as an electrostatic shield, it is possible to prevent sensitivity
of the sensor from being degraded. Further, since the electrostatic
shield can be formed at the same time of forming the common
electrode 28, it is not necessary to separately provide an
electrostatic shield and the electrostatic shield can be easily
formed.
[0074] Note that the present invention is not limited to the above
embodiments.
[0075] Although the multi-ion sensor 1 according to the above
embodiments is provided with the gel internal solutions 14a and 14b
for the sodium ion sensitive membrane 15 and potassium ion
sensitive membrane 16, a concentration ration of sodium ions to
potassium ions can be calculated without the gel internal solutions
14a and 14b. Therefore, the gel internal solutions 14a and 14b may
be omitted in order to reduce the thickness of the planar sensor 4
to be film-like shaped.
[0076] The planar sensor 4 may be disposable goods to be disposed
after using the same, for example, 5 to 10 times. In this case, a
practical slope obtained in advance has been previously written in
a memory chip embedded in the main body 2 or the planar sensor 4 of
the multi-ion sensor 1, and thus a user may perform only a zero
calibration so that the variable A in the Equation (3) becomes 0
mV. At this time, for example, a gelled zero calibration solution
may be previously pasted on a surface where the electrodes of the
planar sensor 4 are formed, whereby the zero calibration may be
carried out by removing the zero calibration solution.
[0077] Regarding each of the Equations (1) to (6), an equivalent
expression that is deformed or the like may be used and the
variable A may be not only a raw value as it is but also may be
added with coefficients and the like.
[0078] In addition, the embodiments and modified embodiment
described above may be partly or entirely combined appropriately
and various modifications are of course possible within the scope
unless departing from the intended spirit thereof.
EXAMPLE
[0079] The following describes the present invention in more detail
by exemplifications, but the present invention is not intended to
be limited to these examples.
[0080] In order to verify the reliability of the multi-ion sensor
according to the present invention, the following tests were
performed.
[0081] <Test>
[0082] First, as a practice test solution, there were prepared a
solution of a known concentration ratio of sodium ions to potassium
ions. In this example, the solution of a sodium ion concentration
being 0.2 mol/dm.sup.3 and potassium ion concentration being 0.05
mol/dm.sup.3 were prepared. As to this test solution, the
concentration ratio of sodium ions to potassium ions was measured
using the multi-ion sensor of the present invention. The
measurement results thereof are shown in Table 2.
TABLE-US-00002 TABLE 2 C.sub.Na 0.2 Mol/dm3 C.sub.K 0.05 Mol/dm3
C.sub.0Na 0.15 Mol/dm3 C.sub.0K 0.03 Mol/dm3 E.sub.Na 17.7 mV
E.sub.K 22.9 mV E.sub.Na - E.sub.K _5.2 mV SlopeNa.sup.+ 57 mV/dec
SlopeK.sup.+ 57 mV/dec C.sub.Na/C.sub.K 4.1
[0083] The concentration ratio of sodium ions to potassium ions
measured by the multi-ion sensor of the present invention using the
values listed in Table 2 was 4.1. Since the concentration ratio of
sodium ions to potassium ions of the practice test solution is 4.0,
it is understood that the concentration ratio of sodium ions to
potassium ions measured by the multi-ion sensor of the present
invention can be an accurate value almost equal to the measured
value.
REFERENCE SIGNS LIST
[0084] 1 . . . Multi-ion sensor [0085] 15 . . . Sodium
ion-sensitive membrane [0086] 16 . . . Potassium ion-sensitive
membrane [0087] 28 . . . Common electrode [0088] 41 . . . Na.sup.+
electrode [0089] 42 . . . K.sup.+ electrode
* * * * *